Get the latest from TODAY

When Ali Rendulic and her husband, Matt, were in their late 20s they decided to start a family. Within a month, Rendulic, then 27, was pregnant and in May of 2013, she gave birth to son, Conner.

When Ali Rendulic and husband Matt started trying for a second child they believed it would be as easy as getting pregnant the first time. But it took three years with several heartbreaking losses before they could conceive a second child. Courtesy Ali Rendulic

“It was just so easy,” Rendulic, 33, of Forrest Hills, Pennsylvania, told TODAY Parents. “We waited like three years and thought ‘Let’s start trying again.’ And we kind of had the same conversation and expected the same results.”

But getting pregnant with a second child wasn’t effortless. About four months later, Rendulic discovered she was pregnant. Soon after, she had a miscarriage. Then they spent another year trying before she became pregnant again. Again, Rendulic miscarried.

Rendulic had unexplained secondary infertility. Secondary infertility, difficulty conceiving after a past pregnancy, likely occurs at the same rate as primary infertility, affecting about 10% of couples.

“Secondary infertility is quite common,” Dr. Meredith Snook, an assistant professor in the Department of Obstetrics, Gynecology and Reproductive Sciences at the University of Pittsburgh, told TODAY Parents. “The best definition is a woman who has been unable to establish a clinical pregnancy after 12 months of having unprotected intercourse, but who has previously had a clinical pregnancy.”

While many patients believe they only have secondary infertility if they have delivered a baby, Snook said that even women who have pregnancies ending in miscarriage experience secondary infertility.

“It is not necessarily that you had to have an actual delivery of a baby. It is that you had a clinical pregnancy, and now you're having a hard time getting pregnant again,” she explained.

Many struggling with secondary infertility feel shocked when becoming pregnant doesn’t happen as naturally as before.

“It can be quite a surprise,” Beall said. “Especially if they conceived very easily at first.”

Stacey Rusch has been struggling with secondary infertility and shares her experiences on her blog. She wants to raise awareness about it and how African-American women experience infertility at higher rates and seek treatment later. Courtesy Instagram/@FrauRusch

That’s exactly what happened to Stacey Rusch. Even though she got pregnant without problem after age 35 with her daughter, she and her husband have been struggling to conceive a second child.

“I didn’t know that two years can be a significant decline in someone’s fertility,” Rusch, a TV lifestyle reporter who shares her journey with infertility on her website, told TODAY. “I thought it would be easy but unfortunately it was not.”

The experts say couples don’t realize only a few years makes a difference when it comes to getting pregnant a second time.

“If you are starting to build your family later on in life, you don’t necessarily want to delay having a second child,” Beall said. “There is a big difference between 37 and 40.”

That’s also why older couples should seek treatment sooner. Women 35 and younger are considered infertile if they’ve not been using contraception for a year and can’t become pregnant. From ages 35 to 40, women should see fertility assistance after six months and women 40 and over should seek help after only three months.

Yet, people with secondary infertility often put off treatment.

“There’s a little bit of denial,” Beall said. “Couples who are struggling with secondary infertility tend to have more guilt, feel as if they are selfish and feel they should be happy with the children they have.”

Rendulic certainly understands this.

“You feel bad for wanting another child,” she said.

Treatments for secondary infertility are the same as to treatment for primary infertility. First, doctors examine both partners to make sure tubes aren't blocked and sperm is moving correctly, for example.

“The male factor component can be assessed with a semen analysis and inquiring about sexual dysfunction," Snook said. "Often with increasing age, we will focus more on assessing a woman's ovarian reserve, which can guide treatment options."

For some patients, like Rendulic, there’s unknown infertility, which means doctors don’t know why the couple can’t conceive. For others, doctors can determine a cause and this influences treatment.

Sometimes women take drugs that boost their ovulation, which is one way to treat it. Rusch opted for in vitro fertilization (IVF), which is considered the most aggressive treatment.

“I understand my chances of having a child is very slim without assistance. The best chance I have is with IVF,” Rusch said.

There’s also intrauterine insemination (IUI), which Rendulic had, where doctors inject sperm into the uterus. She is now pregnant with a second child due at the end of July.

“I have been really thankful,” she said. “I think we evolved as a couple. Three years of what we went through could have really driven us apart.”